Disc drives are commonly used in workstations, personal computers, laptops and other computer systems to store large amounts of data in a form that can be made readily available to a user. Such drives store and retrieve data using one or more magnetizable discs that are rotated at a constant high speed by a spindle motor. Each of the discs has a magnetizable surface coating that can be selectively magnetized by a corresponding read/write head so that the data is stored in the form of magnetic flux transitions along defined data tracks on the surface of the disc.
The heads are suspended over the discs and positionably controlled with respect to the tracks on the discs through the use of a rotary actuator assembly and a servo loop. The servo loop obtains position information from servo fields on the discs and, in response thereto, maintains the radial position of the heads through application of current to an actuator coil. The coil is part of a voice coil motor, which as will be recognized comprises one or more permanent magnets and corresponding pole pieces (magnetically permeable plates) which establish a magnetic field through which the coil moves; the magnetic interaction between the magnetic field of the permanent magnets and magnetic fields established in the coil as a result of the coil current causes the rotary actuator to position the heads as desired over the surfaces of the discs. For additional discussion regarding typical disc drive servo systems, see U.S. Pat. No. 5,262,907 issued Nov. 16, 1993 to Duffy et al. (dedicated servo system) and U.S. Pat. No. 5,136,439 issued Aug. 4, 1992 to Weispfenning et al. (embedded servo system). Both of these references are assigned to the assignee of the present invention.
As will be recognized, a disc drive seek operation comprises the controlled movement of a selected head from an initial track to a destination track. Typically, the velocity of the head during the seek is measured and controlled using a velocity control approach, so that a velocity profile for the head is established and used to adjust the amount of current applied to the coil in order to first accelerate and then decelerate the head towards the destination track. It is desirable to accomplish the seek in as short a time as possible in order to maximize data transfer rates between the disc drive and the host computer; however, the faster the seek, the greater the transitions in the amount of current that must be applied to the coil, which can lead to the undesirable excitation of mechanical resonances in the drive. As will be recognized, such excited resonances can lengthen the time required to settle the head onto the destination track and can also affect the ability of the servo loop to subsequently maintain the head over the destination track. Moreover, such excited resonances, if established in the disc drive base deck or top cover, can further lead to the generation of undesirable acoustic noise.
Efforts have been made in the prior art to minimize such effects, including the addition of acoustic noise dampening materials to the drive structure and the shaping of the velocity profile to minimize the excitation of mechanical resonances during initial portions of the acceleration and deceleration stages of a seek; for example see U.S. Pat. No. 5,475,545 issued Dec. 12, 1995 to Hampshire et al., as well as U.S. Pat. No. 5,657,179 issued Aug. 12, 1997 to McKenzie. Both of these references are assigned to the assignee of the present invention and incorporated herein by reference.
Whereas such prior art approaches have been effective in reducing the excitation of resonances and the generation of acoustic noise, there is a continual need for further improvements to meet the continued demand for drives with ever increasing data storage and transfer rate capacities and ever improving performance characteristics.